Cellular communications systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive voice calls most anywhere they travel. Moreover, as cellular telephone technology has increased, so too has the functionality of cellular devices and the different types of devices available to users. For example, many cellular devices now incorporate personal digital assistant (PDA) features such as calendars, address books, task lists, etc. Moreover, such multi-function devices may also allow users to wirelessly send and receive electronic mail (email) messages and access the Internet via a cellular network and/or a wireless local area network (WLAN), for example.
Even so, as the functionality of cellular communications devices continues to increase, so too does the demand for smaller devices which are easier and more convenient for users to carry. One challenge this poses for cellular device manufacturers is designing antennas that provide desired operating characteristics within the relatively limited amount of space available for the antenna.
External cell phone antennas are advantageous in that they are spaced apart from the user's head, which makes it easier for phone manufacturers to comply with applicable specific absorption rate (SAR) requirements, for example. This is because the farther the radiating element of the cell phone antenna system is from the user, the lower the radiation exposure to the user. Yet, many users prefer internal antennas over external antennas, as external antennas are prone to catch on objects and become damaged, for example. Yet, with the ever increasing trend towards smaller cell phone sizes, for a relatively small phone having an internal antenna, this may place the antenna in relatively close proximity to the user's ear, which may make complying with applicable SAR and/or hearing aid compatibility (HAC) requirements potentially difficult for manufacturers. Further, the reduced space for the antenna may make achieving desired signal characteristics difficult.
One exemplary mobile phone configuration that attempts to address radiation concerns from an internal antenna is set forth in PCT Publication No. WO/2004/021511 A2. The device includes a casing including a first in-built driven antenna element extending a length along a longest side of the casing. Either the portable communication device or the case includes at least one passive beam directive element distanced from and generally extending along at least most of the same length as the first in-built driven antenna element. Because of this, electromagnetic radiation generated by the first in-built driven antenna element is enhanced in a direction away from a side of the casing intended to be facing a user.
Another mobile phone device is disclosed in U.S. Pat. No. 6,920,315 to Wilcox et al. The phone includes multiple radios and multiple antennas located in close proximity to each other, and uses a parallel tuning circuit to optimize the isolation between the antennas. The parallel tuning circuit can include multiple impedance matching circuits to match the impedance in multiple frequency bands or isolating antennas.
Despite the existence of such configurations, further improvements may be desirable in certain applications, particularly where the form factor of the device housing does not provide adequate space for such arrangements. Moreover, as cellular wireless communication systems continue to improve, there is a need for relatively high performance multi-band antennas for operation in EDGE, CODMA and/or WCDMA systems, for example.